1. Field of the Invention
The present invention is related to a tapered teller bearing fitted with a rotational speed detection unit which is used for example to detect the rotational speed of a vehicle wheel.
2. Description of the Related
In order to control an anti-lock braking system (ABS) used to prevent lookup of a wheel when traveling on a slippery road surface, or to control a traction control system (TCS) used to prevent wheel spin when the accelerator is pressed too hard upon moving off or upon turning on a slippery road surface, it is necessary to detect the rotational speed of the wheel. For this reason there has heretofore been proposed rotational speed detection units with various constructions, and some of these are in fact being used.
FIG. 1 shows, as one example of a conventional well-known rotational speed detection unit, a unit which detects the rotational speed of a drive wheel (in general a rear wheel) for example of a heavy vehicle such as a truck. A housing 1 is supported on a vehicle by means of a suspension unit (not shown in the figure) so as not to rotate when running, while a wheel axle 2 has a tip end portion 2a which is inserted into the housing 1. A wheel (not shown in the figure) is fixedly to an outer peripheral surface of the axle 2 at a portion Inwards from the housing 1 in a widthwise direction of the vehicle.
The term "axially" is hereinafter used to mean an axial direction of the axle (left-right direction in FIG. 1).
A pair of axially separated outer range 3 are fixedly attached to an inner peripheral surface of the housing 1, while a pair of axially separated inner rings 4 are fixedly attached to an outer peripheral surface of the axle 2.
Furthermore, a plurality of tapered rollers 5 are provided between the outer ring raceways 6 on the inner peripheral surfaces of the outer rings 3, and the inner ring raceways 7 on the outer peripheral surfaces of the inner rings 4, respectively so as to be freely rotatable therebetween, thus making up a tapered roller bearing 8.
A disk shaped tone wheel 9 is externally fixed to the tip end portion 2a of the axle 2 at its distal end. The tone wheel 9 is made from a magnetic material such as steel, and is formed on its outer side face (right side face in FIG. 1) with alternate ridges and recess around a peripheral direction thereof.
Moreover, a sensor 11 is retained in a holder 19 which is fixedly engaged in an opening portion in an axially outer end of the housing 1. The sensor 11 comprises a permanent magnet 34 magnetized along an axial direction thereof, a pole piece 12 made from a magnetic material, and a coil 13 wound around the pole piece 12. An axially inner end face (left end face in FIG. 1) of the pole piece 12 is faced to the axially outer side face of the tone wheel 9 with a small gap therebetween. The tone wheel 9 and the sensor 11 make up a rotational speed detection unit, which functions in the following manner to detect the rotational speed of the axle 2.
Specifically when the tone wheel 9 rotates together with the axle 2, the gap between the axially outer side face of the tone wheel 9 and the axially inner end face of the pole piece 12 changes, so that the density of the magnetic flux passing through the pole piece 12 changes. As a result, the electromotive force induced in the coil 13 wound around the tone wheel 9 changes sinusoidally. Since the frequency of change of the electromotive force in the coil 13 is proportional to the rotational speed of the axle 2, then if the electromotive force is input as an output signal from the sensor 11, to a control unit for an ABS or TCS, then the ABS or TCS can be controlled.
With the conventional arrangement constructed and used as described above, since the rotational speed detection unit is provided independently as a separate unit from the tapered roller bearing 8, then the number of operations or steps involved in assembling the rotating support portions of the rotational speed detection unit is considerable, and the assembly operation complicated so that not only is cost increased but also miniaturization of the rotating support portions becomes difficult.
Moreover, in order to accurately detect the rotational speed, the dimensions of the small gap between the sensor 11 and the tone wheel 9 must be accurately controlled to meet the design value. However, with the construction wherein the rotational speed detection unit and the tapered roller bearing 8 are provided independently as separate units, the adjustment operation of the small gap is difficult.
To simplify the assembly of the rotating support portions with the rotational speed detection unit installed in it, a construction as shown in FIG. 2, has been disclosed in Japanese Utility Model First Publication KOKAI NO. 2-101274, which eliminates the need for adjustment of the small gap. With this construction, an outer ring raceway 15 is formed on one axial side (left side in FIG. 2) of an inner peripheral surface of an outer ring 14, while an inner ring raceway 17 is formed on the one axial side (left side in FIG. 2) of an outer peripheral surface of an inner ring 16. A plurality of balls 18 ere provided between the outer ring raceway ring 15 and the inner ring raceway ring 17 so as to be freely rotatable therebetween, thus making up a ball bearing.
With regards to the ball bearing constructed in this manner, the other axial side of the outer peripheral surface (right side in FIG. 2) of the inner ring 16 is formed with a pulse generating device 19 which is operated as a tone wheel or pulse ring, while a sensor 20 is mounted on the other axial side of the inner peripheral surface of the outer ring 14 so as to be faced to the pulse generating device 19. This ball bearing with the pulse generating device 19 and the censor 20 assembled in this manner is used with the outer ring 14 fixed end the inner ring 16 rotating. When the inner ring 16 rotates, an output signal from the sensor 20 changes with a frequency proportional to the rotational speed of the inner ring 16.
With the construction disclosed in this publication consideration has been centered on the assembly of a rotational speed detection unit into a ball bearing. However, when applied in this form to tapered roller bearings, which is the subject of the present invention, problems arise in the assembly operation. More specifically, with tapered roller bearings, since there is assembly directionality at the time of assembling the outer ring, inner ring, and tapered roller bearings, then if the tone wheel and the sensor are simply mounted on the inner ring and the outer ring as in FIG. 2, assembly becomes impossible,